The invention relates generally to matrix-addressed x-ray imaging panels, and more particularly, to a system for compensating for amplifier offset and gain artifacts and correcting an image signal generated by a matrix-addressed x-ray imaging panel.
Matrix-addressed x-ray imaging panels composed of amorphous silicon TFT and photodiode arrays have many useful applications in the fields of medicine and industrial inspection. Typically, solid state imaging systems use a two dimensional matrix, or photodiode array, to convert radiation into an image having an intensity proportional to incident radiant energy. In radiation imaging systems used in medical applications, radiation energy passing through, or emanating from, a patient""s body is used for non-invasive in vivo visualization. An example of a high resolution solid state radiation imaging systems for such applications is exemplified by U.S. Pat. No. 5,340,988 assigned to the General Electric Company, the assignee of the instant application. An example of flat panel radiation devices that reduce phantom noise and image artifacts for improving resolution in such imaging systems are described in U.S. Pat. No. 5,610,404, also assigned to the General Electric Company.
In order to obtain a high quality image, corrections must be made to the raw data obtained from the photosensor arrays, including offset and gain corrections related to both the imaging panel and read-out amplifiers connected to the photosensor arrays, to compensate for these effects. In some cases, the gain and offset of different amplifiers may drift with respect to one another due to temperature, electronic pick-up, drifts in regulated voltages and grounds which the amplifiers depend on, etc., resulting in imperfect corrections and line correlated artifacts. Of these contributing factors, temperature is of primary concern. Temperature regulation is generally difficult because of the significant dissipation of heat generated by electronic components. In addition, elevated temperature causes the electrical characteristics of some electronic components to drift. These effects are exacerbated if the imager has an inter-digitated design in which every other line is connected to an amplifier on opposite sides of the imager, which is a common design approach for small pitch detectors found in some mammography panels. In small pitch detectors, line offset artifacts as small as 0.2 counts are clearly seen due to the highly correlated nature of this effect.
During the readout of a given pixel, the gain and offset of the associated readout amplifier may drift with respect to all other amplifiers as a result of temperature effects and a type of electronic pick-up occurring between adjacent data lines within the imaging panel. Such undesirable signals are read out by the amplifier and presented as part of the signal from the addressed pixel.
It is therefore seen to be advantageous that corrections be made to an image signal produced by a matrix-addressed imaging panel exhibiting offset and gain artifacts.
In an exemplary embodiment of the invention, a system for compensating for amplifier offset and gain artifacts and for correcting exposure of image signals generated by a matrix-addressed x-ray imaging panel provides real-time compensation of amplifier offset and gain in integrating read-out amplifiers connected to a matrix-addressed array of photosensors in an imaging panel. The system comprises: an amplifier signal processor coupled to respective readout amplifiers for processing image array signals; an amplifier offset calculator coupled to the amplifier signal processor for averaging values of the amplifier offset signals to yield average amplifier offset signals; a real-time relative gain calculator coupled to the amplifier signal processor for calculating a real time relative gain; an adjusted gain calculator coupled to the real time relative gain calculator for calculating the real time adjusted gain calibration image; and a corrected pixel value calculator coupled to the amplifier offset calculator.